complement activation initiated by the interaction of microbial antigens with complement c3b. When complement factor b binds to the membrane-bound C3b, complement factor d cleaves it to form alternative C3 CONVERTASE (C3BBB) which, stabilized by COMPLEMENT FACTOR P, is able to cleave multiple COMPLEMENT C3 to form alternative C5 CONVERTASE (C3BBB3B) leading to cleavage of complement c5 and the assembly of complement membrane attack complex.